Small flat panel displays are widely used in a variety of applications, including view finders for camcorders and viewing screens for head-mounted displays. One type of device suited for such small displays is the field emission display.
Field emission displays typically include a generally planar emitter beneath a display screen. The emitter is a substrate having an array of surface discontinuities projecting from an upper surface. In many cases, the surface discontinuities are conical projections, or "emitters" integral to the substrate. Typically, the emitters are grouped into emitter sets where the bases of the emitters in the emitter sets are commonly connected. A conductive grid is positioned above the emitters and driven with a voltage of about 30 V-120 V. The emitter sets are then selectively activated by a current path between the bases and ground to produce an electric field extending from the grid to the emitters. In response to the electric field, the emitter sets emit electrons according to the Fowler-Nordheim equation.
The display screen is mounted directly above the grid, and it is coated with a transparent conductive material to form an anode biased to about 1-2 kV. The anode attracts the emitted electrons, causing the electrons to pass through the grid. A cathodoluminescent layer covers the anode to intercept the electrons as they travel toward the 1-2 kV potential of the anode. The electrons strike the cathodoluminescent layer causing the cathodoluminescent layer to emit light at the impact point. The emitted light then passes through the anode and display screen where it is visible to a viewer.
The brightness of the light produced in response to the emitted electrons depends, in part, upon the amount of electrons striking the cathodoluminescent layer in each frame, which in turn depends upon the amount of current available to provide electrons to the emitter sets. The brightness of each area can thus be controlled by controlling the current flow to the respective emitter set. By selectively controlling the current flow to the emitter sets, the light from each area of the display can be controlled and an image can be produced. The light emitted from each of the areas thus becomes all or part of a picture element or "pixel."
In many applications, the size of the field emission display can have significant effects on the cost, reliability, weight, and manufacturability. Generally, the smaller the display, the lower its cost and weight will be. Also, smaller displays typically have higher reliability and higher manufacturing yields. However, the size of the display can be limited by the size and number of pixels in the array. For example, for a conventional array having 240 rows of pixels, the minimum vertical screen dimension is 240 times the minimum height of the pixels.
One way to reduce the minimum vertical dimension of the display is to eliminate the uppermost ten lines and lowermost ten lines of the display. The elimination of these 20 lines "chops" the top and bottom of the image, causing a noticeable loss of picture quality.